Radiation sensors provide a wide variety of functionality in both military and commercial applications. For example, radiation sensors are utilized in communication systems, in lighting control systems, and in imaging systems, just to name a few. In many applications, the radiation sensor is mounted to a surface so that the angular field of view (FOV) of the sensor does not intersect the surface, that is, the sensor is configured to detect radiation incident on the surface to which the sensor is mounted. The sensor is typically configured so that its FOV is directed into open space for the detection of incident radiation, without reflection off the surface to which the sensor is mounted. Examples of such sensors can be found in one or more of U.S. Pat. Nos. 2,964,636, 4,636,631, and 5,308,985.
Nonetheless, it may be desirable in many applications to detect and measure radiation reflected off a surface to, for instance, control the reflected radiation intensity (radiance) or characterize the reflectivity of the surface. For example, in a radiant heating system where reflective surfaces are utilized to redirect the radiant heat flux it may be desirable to precisely monitor the intensity of the radiation reflected at several points on the surfaces. Monitoring the intensity of the reflected radiation or changes in reflectivity may be important in order to accurately establish and control radiant intensity or uniformity, or to establish and maintain a desired spatial intensity pattern. It may also be desirable to monitor the degradation in the reflectivity of the reflective surfaces over time, especially where the cumulative effect may be significant. This would be possible using a known incident radiant intensity and a calibrated reflected radiance sensor.
As another example, it may be desirable to precisely control the intensity (luminance) reflected off of surfaces in lighting systems used in a factory, office, aircraft, etc. The reflectivity of surfaces degrade through exposure to the elements of nature and normal use, which may decrease their ability to effectively reflect light onto the subject of interest. In addition, the intensity of the light source may change over time, and thus causing a reduction in reflected luminance. Source intensity degradation also applies to radiant heating systems. By monitoring the reflected radiance or luminance, the source intensity can be precisely controlled to compensate for source intensity changes and surface reflectance changes. These are just two examples of the many circumstances in which it may be desirable to measure the radiance or luminance reflected off a surface, and it will be appreciated by those of ordinary skill in the art that numerous other circumstances exist in which it would be desirable to measure reflected radiation.
However, in order to detect the radiation reflected off a surface, a probe or other means is typically utilized to position the sensor over the surface so the FOV of the sensor is directed toward the general area of interest of the surface. However, the probe or other means used to position the sensor may interfere with or possibly block a portion of the incident radiation. Moreover, the reflected radiation incident on the sensor may be redirected toward the surface in a manner that produces multiple reflections before reaching the sensor, which may cause inconclusive sensor readings. The probe may also not be capable of being precisely and consistently positioned over the surface so as to render conclusive measurements. Thus, the amount of radiation reflected off the surface may not be accurately measured, and therefore, may be irrelevant. Usually, reflected radiation is remotely measured with radiometer instruments, which are expensive, bulky, and can block some of the incident radiation. Furthermore, they are not integrated with the surface so that they may be operated continuously for uninterrupted monitoring which advantageous in critical control situations.
Therefore, an unsatisfied need exists in the industry for a sensor for accurately and consistently measuring the radiation reflected off a surface.